Method for forming highly reactive olefin functional polymers

ABSTRACT

A process for the preparation of polybutene having an exo-olefin content of at least 50 mol. % from an isobutene-containing monomer feedstock, which process comprises contacting said isobutene-containing feedstock with a Lewis acid catalyst complexed with a Lewis base, in an apolar polymerization medium, and initiating polymerization of said isobutene-containing feedstock. The Lewis acid catalyst is of formula R′AlCl 2 , wherein R′ is hydrocarbyl; the Lewis base is a dihydrocarbyl ether wherein each hydrocarbyl group is independently selected from C1-C8 hydrocarbyl groups and one or both hydrocarbyl groups of the dihydrocarbyl ether are substituted with an electron-withdrawing group; and the initiator is a compound of formula RX, wherein X is a halide; R is a hydrocarbyl group capable of forming a stable carbocation, and the carbon linking group R to group X is tertiary, benzylic, or allylic.

The invention is directed to an improved process for the preparation of polybutene having an exo-olefin content of at least 50 mol. % by the polymerization of iso-butene, or a C₄ feed comprising iso-butene and other C₄ olefins using (i) a Lewis acid⋅Lewis base catalyst complex and an alkyl halide initiator capable of initiating cationic polymerization, in a substantially or completely apolar polymerization medium, where the catalyst complex is pre-activated with water. Surprisingly, in the above polymerization reaction, it has been found that the addition of from about 0.1 to about 1 equivalent of a trialkyl aluminum to the pre-activated catalyst improves the polydispersity of the resulting HR-PIB product without adversely effecting terminal vinylidene content and molecular weight.

BACKGROUND OF THE INVENTION

Dispersants based on polybutene succinimides are ubiquitous in lubricating oils worldwide. An essential step in the manufacture of these dispersants is maleation of polybutene to polybutene succinic anhydride, which is further aminated with a polyamine to produce the succinimide. The maleation process is facilitated by polyisobutylene (PIB) with a high level of vinylidene at the polymer terminus, which can react smoothly with maleic anhydride in a thermal or “ene”, without the need for chlorine as a facilitator. Such polymers, termed highly reactive PIB or HR-PIB, are preferred in industry for their process, performance and environmental benefits.

Existing processes to manufacture HR-PIB via cationic polymerization of isobutylene (IB) utilize a BF₃ catalyst associated with a range of alcohols and/or ethers often requiring pure IB feed, very low temperatures, and fluorine clean-up steps (Mach et al. Lubr. Sci. 1999 11(2) 175-185). Such processes can be costly in terms of both equipment and operations. More recently, catalysts based on AlCl₃ or alkyl AlCl₂ Lewis acids (LA) complexed with ether Lewis bases (LB) have shown the capability to produce HR-PIB in the presence of alkyl halide initiators (see review by Kostjuk, RSC Adv., 2015, 5, 13125-13144). The Lewis acid ionizes the initiator to start polymerization, and the Lewis base deprotonates the polymeric carbenium to the desired olefin. The binding strength of the LA*LB complex is dependent on the nature of LA and LB as well as on the environment. In a relatively polar medium such as dichloromethane (DCM), a Lewis acid⋅Lewis base complex of EtAlCl₂ (EADC) and di-isopropyl ether is able to produce HR-PIB with high vinylidene levels. However, in the apolar, all hydrocarbon environment of a C₄ polymerization reactor, the above complex is too strong and the Lewis acid is unable to ionize t-butyl chloride (t-BuCl), a common initiator used to start polymerization of IB.

Adjustment of the complexation energetics via introduction of electron withdrawing groups into the Lewis base as in bis-(2-chloroethyl) ether (CEE), results in efficient ionization of t-BuCl and initiation of IB polymerization even in apolar media, while still maintaining high vinylidene content (U.S. Pat. No. 9,156,924). The amount of reactive vinylidene olefin (exo olefin) produced is dependent on the rate of deprotonation of the polymeric carbenium ion relative to the rate of isomerization to more hindered ions that lead to less reactive olefins. Therefore, a high concentration of the CEE deprotonation agent is normally used to maximize the vinylidene content (e.g. 1.5-3 times the LA concentration).

A high concentration of CEE, however, can decrease the rate of IB polymerization because it inhibits dissociation of the LA*CEE complex which dissociation is required to ionize the t-BuCl initiator. Long residence times and large reactors would then be required to realize commercially reasonable monomer conversions. The high rate of deprotonation also lowers the molecular weight (MW) of the polymer product because it interrupts chain growth. Therefore, a means to simultaneously achieve high terminal vinylidene, high monomer conversion and high MW simultaneously using aluminum based catalysts at reasonable temperatures would be very valuable to the industry.

U.S. Pat. No. 7,411,104 teaches the addition of tertiary alcohols such as t-butanol in combination with a secondary alkyl ether, such as di-isopropyl ether, during the polymerization of IB using a BF₃ catalyst to enhance the vinylidene content of the resulting HR-PIB polymer. This type of ether does not work with an aluminum based system, however, because the Lewis acid-Lewis base complex is too strong and polymerization is impeded (Macromolecules 2014, 47, 1959-1965). U.S. Pat. No. 7,411,104 further teaches that the ratio of secondary alkyl ether to tertiary alcohol used in that process must be in the range of 0.5-1.2 and if the mole ratio is “less or more than the above-mentioned range, the content of the terminal vinylidene decreases, and the advantageous effect of the present invention cannot be achieved”. In an aluminum-based system, however, such a large amount of tertiary alcohol would act as a poison, reducing conversion to low and commercially impractical levels.

U.S. Pat. No. 10,174,138 teaches that, in a polymerization process for the preparation of polybutene by polymerization of iso-butene, or a C₄ feed comprising iso-butene and other C₄ olefins using AlCl₃ or alkyl AlCl₂ Lewis acids (LA) complexed with ether Lewis bases having an electron-withdrawing group (LB) as the catalyst and an alkyl halide initiator, in a substantially or completely apolar polymerization medium, the presence of a tertiary alcohol, when used in relatively small amounts, will increase the terminal vinylidene content of the resulting polybutene product without causing a corresponding reduction in molecular weight.

U.S. Pat. Nos. 10,047,174 and 10,167,352 teach that, in a polymerization process for the preparation of polybutene by polymerization of iso-butene, or a C₄ feed comprising iso-butene and other C₄ olefins using AlCl₃ or alkyl AlCl₂ Lewis acids (LA) complexed with ether Lewis bases having an electron-withdrawing group (LB) as the catalyst and an alkyl halide initiator, in a substantially or completely apolar polymerization medium (and in both the presence and absence of oxygenate impurities in the monomer feed), the pre-activation of the catalyst with small amounts of water allows for steady state and high yields of HR-PIB, particularly when using a continuous reaction, such as a continuous reaction performed using a continuous stirred tank reactor (CSTR).

It was found, however, that HR-PIB derived from a continuous process using catalyst pre-activated with water tended to have a relatively high polydispersity index (PDI) of about 3 or above, which is substantially higher than the PDI of commercially available HR-PIB produced via cationic polymerization of isobutylene (IB) utilizing BF₃ catalyst. It was found that the PDI value was not significantly improved by increased mixing during the reaction or by modifying the reaction temperature or pressure, which indicates that the elevated PDI was related to the specific catalyst system chemistry.

An increase in the PDI of HR-PIB used to form dispersants may result in an increase in the viscosity of additive packages and lubricants formulated with such dispersants, which is a great disadvantage, particularly in an industry in which the trend is leading to lower viscosity lubricating oil compositions providing improved fuel economy performance. A method for the control of HR-PIB PDI using mixed ethers together with ethyl aluminum dichloride (EADC) was previously reported (Kostjuk et al., Polymer 99, 2015, 633-641). However, the lowest PDI obtained via that method was 2.4, which remains above the industry standard value of 1.8 to 2.2.

DETAILED DESCRIPTION OF THE INVENTION

Lewis acids useful in the practice of the present invention include Lewis acids of the formula R′AlCl₂, wherein R′ is a hydrocarbyl group, preferably a hydrocarbyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 12 carbons. As used herein, the term “hydrocarbyl” means a chemical group of a compound that contains hydrogen and carbon atoms and that are bonded to the remainder of the compound directly via a carbon atom. The group may contain one or more atoms other than carbon and hydrogen (“hetero atoms”), provided such hetero atoms do not affect the essentially hydrocarbyl nature of the group.

Useful Lewis bases are dihydrocarbyl ethers wherein each hydrocarbyl group is independently selected from hydrocarbyl groups having 1 to 8 carbon atoms. The hydrocarbyl groups of the ether may be branched, straight-chained or cyclic. Where the hydrocarbyl groups of the ether are branched or straight-chained, the hydrocarbyl groups are preferably alkyl groups, more preferably alkyl groups having 1 to 4 carbon atoms. One or both hydrocarbyl groups of the dihydrocarbyl ether are substituted with an electron withdrawing group, particularly a halogen atom, preferably a chlorine atom.

The Lewis acid and Lewis base can be complexed by, for example, by dissolving the Lewis acid in a solvent selected from liquid, apolar, non-halogenated aliphatics, and liquid aromatics, such as benzene, chlorobenzene, toluene and xylene, to form a solution and then adding the Lewis base to the solution, while the solution is stirred. The complex may be added to the polymerization medium with the solvent; alternatively, the solvent may be removed prior to the addition of the complex to the polymerization medium. Preferably, the solvent is a non-halogenated aliphatic or aromatic solvent, and is more preferably xylene or toluene or mixed C₄ to C₁₂ linear and/or branched hydrocarbons (e.g., ISOPAR™, available from ExxonMobil Corporation), most preferably toluene or mixed C₄ to C₁₂ linear and/or branched hydrocarbons. When the Lewis acid and Lewis Base are complexed in xylene or toluene, it is preferable to dissolve the Lewis base in the xylene or toluene solvent to form a solution, and then add the Lewis acid to the Lewis base solution, while the solution is stirred.

The molar ratio of Lewis acid to Lewis base in the complex will typically be maintained within a range of from about 1:1 to about 1:8, preferably from about 1:1 to about 1:8, more preferably from about 1:1 to about 1:6, such as about 1:1 to about 1:3 (e.g. about 1:1.5).

To provide pre-activation, water may be added to the Lewis acid⋅Lewis base complex, which is then allowed to age for a period of time before being brought into contact with the feedstock. Water may be added to the Lewis acid/Lewis base complex in an amount of from about 0.02 to about 10 equivalents of water per equivalent of Lewis acid, preferably from about 0.03 to about 0.2 (such as from about 0.05 to about 0.15) equivalents of water per equivalent of Lewis acid. The activating water may be introduced to the Lewis acid⋅Lewis base complex via a saturated solution in toluene, which may be done at room temperature. Alternatively, the water may be introduced directly, if dissolved in the Lewis base. This second route allows the catalyst complex to be prepared in neat apolar, non-halogenated aliphatic solvent (e.g., hexane), eliminating the need to introduce an aromatic solvent (e.g., toluene) into the complex. After addition of the water, the Lewis acid⋅Lewis base complex is preferably allowed to sit for a period of time before use in order to allow the water to pre-activate the complex. Activation times may be from 1 minute to one day, preferably from about 2 minutes to about 3 hours, such as from about 5 minutes to about 60 minutes. Preferably, during activation, the complex can be maintained at a temperature of from about −10° C. to about 20° C.

In accordance with the present invention, the water treated, pre-activated catalyst complex is then reacted with from about 0.1 to about 2, preferably from about 0.2 to about 1.5, more preferably from about 0.3 to about 1.0 molar equivalents of a trialkyl aluminum (R″₃Al, wherein R″ is an alkyl group having 2 or more carbon atoms) per equivalent of Lewis acid. Suitable trialkyl aluminums include, for example, trioctyl aluminum, triisobutyl aluminum and triethyl aluminum.

While not wishing to be bound by any specific theory, it is believed that the addition of water to the catalyst complex converts a portion of the R′AlCl₂ Lewis acid to the corresponding chloroaluminum oxane (CAO), which results in improved activity, but reduced solubility in the monomer feed (which may result in the increased PDI of the HR-PIB product), and that the solubility of the pre-activated catalyst complex is restored by reaction with the trialkyl aluminum (resulting in a reduced PDI). Two possible reaction schemes are shown below. In both, the Lewis acid is EtAlCl₂ (EADC), and the Lewis base is a chlorinated dihydrocarbyl ether (CEE). In scheme 1, the water is added after formation of the Lewis acid⋅Lewis base complex via a saturated solution in toluene. In scheme 2, the water was introduced directly, dissolved into the Lewis base in hexane.

An “initiator” is defined as a compound that can initiate polymerization, in the presence or absence of adventitious water and in the presence of a proton trap. The initiator of the present invention (RX) comprises a hydrocarbyl R group, preferably an alkyl or aryl-alkyl group, wherein the carbon linking group R to X is tertiary, benzylic or allylic, preferably tertiary, which hydrocarbyl group can form a stable carbocation (e.g., t-butyl⁺); and an X group, which is a halide, preferably chlorine.

The polymerization medium must be a substantially or completely apolar polymerization medium, such as a mixture of saturated and unsaturated C₄ hydrocarbons.

In the polymerization process of the present invention, the feedstock may be pure isobutylene or a mixed C₄ hydrocarbyl feedstock containing isobutylene, such as a C₄ cut resulting from the thermal or catalytic cracking operation of, for example, naphtha. Thus, suitable feedstocks will typically contain at least 10%, and up to 100% isobutylene, by mass (e.g. 20-50%, based on the total mass of the feed). In addition to isobutylene, conventional C₄ cuts suitable for use as feedstocks that are of industrial importance typically will contain between about 5% and about 50% butene-1, between about 2% and about 40% butene-2, between about 2% and about 60% iso-butane, between about 2% and about 20% n-butane, and up to about 0.5% butadiene, all percentages being by mass, based on the total feed mass. Feedstocks containing isobutylene may also contain other non-C₄ polymerizable olefin monomers in minor amounts, e.g., typically less than 10%, preferably less than about 5%, and most preferably less than 1%, such as propadiene, propylene and C₅ olefins. The feedstock may contain various polar feed impurities such as acetone, methanol, acetonitrile, propionic acid, but will preferably be purified so that the feedstock contains less than 5 ppm, such as less than 4 ppm or 3 ppm or 2 ppm or 1 ppm or 0.5 ppm of polar impurities.

The term “polybutene”, as employed herein is intended to include not only homopolymers of isobutylene, but also copolymers of isobutylene and one or more other C₄ polymerizable monomers of conventional C₄ cuts as well as non-C₄ ethylenically unsaturated olefin monomers containing 5 carbon atoms, provided such copolymers contain typically at least 50 mass %, preferably at least 65 mass %, and most preferably at least 80 mass % isobutylene units, based on the polymer number average molecular weight (M _(n)).

The amount of the Lewis acid⋅Lewis base complex employed in the process of the present invention can be controlled, in conjunction with the concentration of initiator and monomer, reaction time and temperature, to achieve the target M _(n) of the polybutene polymer product, the conversion of iso-butene and yield of polybutene. In view of the above, the Lewis acid⋅Lewis base complex is typically employed in an amount sufficient to contact the butene monomer in a liquid phase reaction mixture at a concentration of millimoles of Lewis acid⋅Lewis base complex per liter of reaction mixture of from about 0.2 mM to about 200 mM, such as from about 1 mM to about 200 mM, preferably from about 5 mM to about 100 mM, and more preferably from about 10 mM to about 50 mM, such as about 10 mM to about 30 mM.

The initiator will typically be employed in a liquid phase reaction mixture comprising the iso-butene monomer at a concentration of millimoles of initiator per liter of medium, and independent from the amount of Lewis acid⋅Lewis base complex, of from about 1 mM to about 500 mM, preferably from about 2 mM to about 300 mM, and more preferably from about 2 mM to about 200 mM, such as about 10 mM to about 30 mM.

The polymerization reaction can be performed as a batch or continuous process. On an industrial scale, the polymerization reaction is preferably conducted continuously. The continuous process can be carried out in tubular reactors, tube-bundle reactors or loop reactors, or tube or tube-bundle reactors with continuous circulation of the reaction material, or in a stirred tank reactor (glass, carbon steel or Monel preferred), a pump around loop, a plugged flow reactor or a combination thereof.

The polymerization reaction is conducted in the liquid phase to induce linear or chain-type polymerization, as opposed to ring or branch formation. Thus, if a feed is used that is gaseous under ambient temperature, it is preferred to control the reaction pressure and/or dissolve the feed in an inert solvent or liquid diluent, in order to maintain the feed in the liquid phase. Typical C₄ cuts comprising the feed are liquid under pressure and do not require a solvent or diluent. Typical diluents suitable for use with the process include C₃ to C₆ alkanes, such as propane, butane, pentane and isobutane.

The Lewis acid⋅Lewis base complex is typically introduced into the reactor as a liquid partially or completely dissolved in a solvent, or as a solid. Polymerization is preferably conducted at a pressure sufficient to maintain the C₄ feed in a liquid state at the reaction temperature, or at higher pressures. The initiator may be introduced to the monomer feed or the reaction mixture in liquid form together with the Lewis acid-Lewis base complex or, preferably, is introduced to the monomer feed or the reaction mixture in liquid form by a line separate from the Lewis acid-Lewis base complex addition line.

The liquid phase reaction mixture temperature is controlled by conventional means to be typically from about −30° C. to about +50° C., preferably from about −10° C. to about +30° C., more preferably from about −5° C. to about +20° C., such as about 0° C. to about +15° C. to minimize refrigeration costs and unwanted side reactions.

In order to insure even distribution of the catalyst within the reactor, turbulent flow of the reactor contents (Reynolds number >100, preferably >1000) can be generated by mixing, or with suitable baffles, such as baffle plates or oscillating baffles, or by dimensioning the reactor tube cross sections so that a suitable flow velocity is established.

The steady state residence time of the butene to be polymerized may be from about 1 to about 300 minutes, such as 2 to about 120 minutes, preferably from about 4 to about 60 minutes or from about 5 to about 45 minutes (e.g., from about 6 to about 30 minutes).

The process of the present invention is typically conducted in a manner achieving an isobutylene conversion in the range of from about 20% up to about 100%, preferably from about 50% to about 100%, and more preferably from about 70% to about 100%, such as 80% to 100%, 90% to 100% or 95% to 100%. The combined use of temperature control and catalyst feed rate permits formation of polybutenes having a M _(n) of from about 400 Daltons to about 4000 Daltons, preferably from about 700 Daltons to about 3000 Daltons, more preferably from about 1000 Daltons to about 2500 Daltons; a molecular weight distribution (MWD) of typically from about 1.1 to about 4.0, preferably from about 1.5 to about 3.0, an exo-olefin content of greater than 50 mol. %, preferably greater than 60 mol. %, more preferably greater than 70 mol. %, such as from about 80 mol. % to about 95 mol. %; a tetra-substituted olefin content of less than about 20 mol. %, such as less than about 15 mol. %, preferably less than about 10 mol. %, more preferably less than about 5 mol. %; and a chlorine content of less than about 10 mol. %, such as less than about 5 mol. %, preferably less than about 2 mol. %, more preferably less than about 1 mol. % based on the total moles of polymer.

Once the target molecular weight of the polymer is achieved, the polymer product can be discharged from the reactor and passed into a medium that deactivates the polymerization catalyst and terminates the polymerization. Suitable deactivation media include water, amines, alcohols and caustics. The polyisobutylene product can then be separated by distilling off the remaining C₄ hydrocarbons and low molecular weight oligomers. Preferably residual amounts of catalyst are removed, usually by washing with water or caustic.

In one commercially preferred embodiment (from a standpoint of performance, environmental impact and cost), the Lewis acid is R′AlCl₂, wherein R′ is C₁ to C₄ hydrocarbyl, specifically, MeAlCl₂, EtAlCl₂(EADC), iso-BuAlCl₂ or n-BuAlCl₂, the Lewis base is a chlorinated dihydrocarbyl ether (CEE), the solvent is ISOPAR or toluene, and the complex is formed by dissolving the Lewis base, or the Lewis base and water in the solvent to form a solution and then adding the Lewis acid to the Lewis base solution in an amount such that the molar ratio of Lewis acid to Lewis base in the complex is from about 1:1 to about 1:1.5.

This invention will be further understood by reference to the following examples, which are not intended, and should not be construed as listing all possible embodiments within the scope of the invention.

Example 1 (Comparative)

Ethyl aluminum dichloride (EADC)•chlorinated dihydrocarbyl ether (CEE) complex was prepared in a N₂ atmosphere glove box. An appropriate amount of EADC in hexane (1M) was mixed with CEE in a 1:2 molar ratio. Toluene containing 0.075 equivalents of H₂O relative to EADC was added to the complex to form a 0.1M complex solution. The catalyst solution was delivered to the CSTR via a SS syringe pump. The initiator was delivered as a tBuCl solution in hexane via another SS Syringe pump. The feed, synthetic Raffinate-1 containing 40% IB, was passed through a 3A and AZ300 column before introduction into the CSTR. The Raffinate-1 feed had less than 0.5 ppm polar (oxygenate) impurities, as determined by ASTM D7423. The initial concentrations of reagents were [H₂O]=0.73 mM, [EADC]=0.01M, [CEE]=0.02M, [tBuCl]=0.02M, before reaching a final steady state concentration of IB of 11% after three residence times of 20 minutes. Mixing in the reactor was provided by a rotating 1000 rpm impeller. The pressure in the reactor was maintained to 50 psig and the polymerization temperature was 4° C. The reaction mixture at the CSTR exit was quenched at 4° C. with a mixture of isopropanol/water (80/20, v/v). 72% monomer conversion was observed, and the resulting HR PIB product had Mn(GPC)=1600, PDI=2.72; 74% exo-olefin functionality, determined by 13C NMR.

Example 2 (Inventive)

Example 2 was performed as in Example 1, except that 0.5 molar equivalents of trioctyl aluminum, relative to EADC, were added to the catalyst. 95% monomer conversion was observed, and the resulting HR PIB product had Mn(GPC)=1400, PDI=2.24; 61% exo-olefin functionality, determined by 13C NMR.

Example 3 (Invention)

Example 3 was performed with the Example 1 reagent concentrations, in a 20 minutes minibatch run. EADC•CEE was 1:1.5, and a feed of 8% isobutylene in hexane was used; and [tBuCl]=0.01M. The catalyst complex was prepared in toluene and 1.0 equivalent of trioctyl aluminum, relative to EADC, was added after pre-activation of the catalyst complex with 0.1 equivalents of water. 59% monomer conversion was observed, and the resulting HR PIB product had Mn(GPC)=1300, PDI=2.29; 65% exo-olefin functionality, determined by 13C NMR.

Example 4 (Inventive)

Example 4 was performed with the Example 3 reagent concentrations, except that 0.5 equivalents of trioctyl aluminum were used. 53% monomer conversion was observed, and the resulting HR PIB product had Mn(GPC)=1600, PDI=2.40; 73% exo-olefin functionality, determined by 13C NMR.

Example 5 (Comparative)

Example 5 was performed in the same manner as Example 3, but with no trioctyl aluminum added. 100% IB conversion was observed, and the resulting HR-PIB product had Mn(GPC)=937, PDI=3.92, 74% exo-olefin functionality, determined by 13C NMR.

Example 6 (Inventive)

Example 6 was performed in the same manner as Example 3, except that 1.0 equivalent of triisobutyl aluminum, relative to EADC, was added instead of trioctyl aluminum. 31% IB conversion was observed and the final HR PIB product had Mn=1000, PDI=1.95; 85% exo-olefin functionality, determined by 13C NMR.

Example 7 (Inventive)

Example 7 was performed in the same manner as Example 3 except that hexane was used during preparation of the catalyst complex. Water (1 μL, 0.05 equivalents, relative to EADC) was added to 176 μL of CEE and mixed. 8.5 mL of hexane was then added followed by the addition of 1 mL 1M EADC in hexane. 0.25 equivalents (relative to EADC) of trioctyl aluminum were then added. 58% IB conversion was observed and the final HR PIB product had Mn=1560, PDI=2.28; 81% exo-olefin functionality, determined by 13C NMR.

While certain representative embodiments and details have been provided to illustrate the invention, it will be apparent to the skilled artisan that various product and process changes from those disclosed herein may be made without departing from the scope of the present invention. The appended claims define the scope of the invention

All cited patents, test procedures, priority documents, and other cited documents are fully incorporated by reference to the extent that such material is consistent with this specification and for all jurisdictions in which such incorporation by reference is permitted.

Certain features of the present invention are described in terms of a set of numerical upper limits and a set of numerical lower limits. This specification discloses all ranges formed by any combination of these limits. It is to be understood that the upper limits and lower limits, as well as range and ratio limits set forth herein may be independently combined, and that all combinations of these limits are within the scope of the invention unless otherwise indicated. 

What is claimed is:
 1. A process for the preparation of polybutene having an exo-olefin content of at least 50 mol. % from an isobutene or an isobutene-containing monomer feedstock, which process comprises contacting said isobutene or isobutene-containing feedstock, with a Lewis acid catalyst complexed with a Lewis base, in a substantially or completely apolar polymerization medium, and initiating polymerization of said isobutene or isobutene-containing feedstock with an initiator, wherein said Lewis acid catalyst is a Lewis acid of the formula R′AlCl₂, wherein R′ is a hydrocarbyl group; said Lewis base is a dihydrocarbyl ether wherein each hydrocarbyl group is independently selected from hydrocarbyl groups having 1 to 8 carbon atoms and one or both hydrocarbyl groups of the dihydrocarbyl ether are substituted with an electron withdrawing group and the initiator is a compound of the formula RX, wherein X is a halide; R is a hydrocarbyl group capable of forming a stable carbocation, and the carbon linking group R to group X is tertiary, benzylic or allylic; wherein the catalyst complex is pre-activated by addition of water, and the pre-activated catalyst complex is subsequently reacted with from about 0.1 to about 2 molar equivalents, per equivalent of Lewis acid, of a trialkyl aluminum compound wherein each alkyl group of said trialkyl aluminum compound has at least 2 carbon atoms.
 2. The process of claim 1, wherein R′ is an alkyl group having 1 to 12 carbons.
 3. The process of claim 1, wherein said Lewis base is dihydrocarbyl ether wherein each hydrocarbyl group is independently selected from hydrocarbyl groups having 1 to 8 carbon atoms and one or both hydrocarbyl groups of the dihydrocarbyl ether are substituted with a chlorine atom.
 4. The process of claim 3, wherein said Lewis base is a dihydrocarbyl ether wherein each hydrocarbyl group is independently selected from alkyl groups having 1 to 4 carbon atoms and one or both hydrocarbyl groups of the dihydrocarbyl ether are substituted with a chlorine atom.
 5. The process of claim 1, wherein the Lewis acid and Lewis base are complexed in a solvent selected from the group consisting of mixed C₄ to C₁₂ linear and/or branched hydrocarbons, toluene, and xylene.
 6. The process of claim 1, wherein said apolar polymerization medium is selected from saturated C₄ hydrocarbons, unsaturated C₄ hydrocarbons, and mixtures thereof.
 7. The process of claim 1, wherein said isobutene or isobutene-containing feedstock is selected from pure isobutene; a C₄ refinery cut containing between about 20-50% isobutene, between 5% and about 50% butene-1, between about 2% and about 40% butene-2, between about 2% and about 60% iso-butane, between about 2% and about 20% n-butane, and up to about 0.5% butadiene, wherein all percentages are by mass, based on the total mass of the C₄ refinery cut; and mixtures of pure isobutene and said C₄ refinery cut.
 8. The process of claim 1, wherein said catalyst complex is pre-activated by addition of from about 0.02 to about 10 equivalents, per equivalent of Lewis acid, of water.
 9. The process of claim 1, wherein said Lewis acid catalyst complexed with a Lewis base, is contacted with said isobutene or isobutene-containing feedstock at a concentration of millimoles of Lewis acid-Lewis base complex per liter of feedstock of from about 0.2 mM to about 200 mM.
 10. The process of claim 1, wherein the polymerization process is conducted continuously.
 11. The process of claim 1, wherein said polybutene product has an exo-olefin content of at least 70 mol. %.
 12. The process of claim 1, wherein said polybutene has a number average molecular weight (M_(n)) of from about 400 Daltons to about 4000 Daltons.
 13. The process of claim 1, wherein said trialkyl aluminum compound is selected from the group consisting of trioctyl aluminum, triisobutyl aluminum, triethyl aluminum, and mixtures thereof. 